This application relates generally to methods of attaching objects together and more particularly to methods of securing an assembly containing electronics inside a hollow shell.
In many instances, it is necessary to secure an assembly containing electronic components inside a protective shell. This need arises because the electronic components must be exposed while they are being assembled but must be covered by a protective shell when in use.
Various methods of securing an assembly inside a shell are known. One method is to cut a tab at the open end of the shell. Once the assembly is inside the hollow shell, the tab is folded down to partially block the opening of the shell. This method, however, is only useful if the shell is to remain open at the end. In many instances, it is unacceptable to allow the electronics to be exposed to the environment at the ends of the shell. Further, when exposed to high G forces, the assembly tends to slip out from the shell.
Another technique of securing an assembly inside a shell is called "magnaforming". In this technique, a thin metal shell is propelled explosively at the assembly. The metal wraps securely around the assembly, forming a protective cover. One disadvantage of this technique is that the metal is propelled as a result of the release of energy in a large capacitive discharge. The capacitive discharge, however, may damage electronic components and magnaforming is not appropriate for securing an electronic assembly in a cover.
Screws are also used for securing assemblies inside protective covers. However, where the screws are used to secure an assembly into a this walled cover, very small flat head screws must be used if the screws are to be flush with the surface of the cover. Very small screws, however, are fragile and prone to damage at assembly. Alternatively, if larger screws are used, the screws will protrude beyond the cover. Such an arrangement is not desirable if the assembly must move since the protruding screws tend to get caught on other objects.
Another technique for securing an assembly inside a cylindrical shell is called "ring swaging". According to this technique, a groove is machined into the assembly before it is placed inside the shell. The shell is then deformed to protrude into the groove, thereby securing the assembly. This technique, however, leaves a groove along the outside of the cover. As with screws, this groove can get caught if the assembly with its grooved outer shell moves relative to other components.
Some form of adhesive could be used to secure the assembly to the shell. However, assembling parts with adhesive is sometimes difficult. The manufacturing complexity of using adhesive makes this technique undesirable.
More complicated schemes for securing an assembly inside a cover are also known. For example, split rings or locking rings are sometimes used. However, these techniques, because they require added components, add complexity, cost, packaging volume, and weight to the finished product. These attributes are often undesirable.
The need for securing an electronics assembly in a shell acting as a protective cover is particularly acute in a military environment. One such example is an electronic decoy. Decoys contain an electronic assembly which produces RF signals similar to what are produced by a plane, ship, tank, or some other piece of military hardware. Enemy RF receivers are, thus, deceived into reporting the presence of military hardware which is not in fact present. Enemy fire is drawn towards the decoy rather than at real military hardware.
Decoys are often propelled into a desired position. Thus, whatever means are used to secure the payload inside the shell must be able to withstand high G forces. Moreover, where the decoy is propelled from a launcher, the decoy can contain no protruding screws or grooves which could get caught in the launcher. Further, since decoys are expendable, the decoy must be made as inexpensively as possible.
Based on the requirements for a decoy, all the known methods of securing an electronics assembly to a cover suffer at least one shortcoming.